High performance anchors used to moor sea surface vessels and other structures need to be embedded into the seafloor a sufficient depth in order to develop the required holding capacity. Two general methods have been developed over time for this purpose, to wit, drag-embedment and direct-embedment techniques. The method of drag-embedment involves either hauling-in or horizontal movement of the top of the mooring line such that the anchor attached to the lower end of the mooring line is moved horizontally; the anchor is designed such that horizontal movement causes the anchor to dive below the seafloor. The anchor will cease diving below the seafloor when an equilibrium between its holding capacity and the mooring line tension is reached. Methods of direct-embedment of anchors to their final penetration depth include the use of gravity, ballistics, hammers (impact and vibratory) and suction. Gravity has been used to accelerate anchors in free-fall and to force them into the seafloor with gravity followers. Ballistic anchors use a propellant to penetrate the anchors into the seafloor while suction is used in conjunction with suction pile (or suction follower) outfitted with a plate anchor at its tip. The suction follower in the latter case is only an installation tool and is removed after embedding the anchor to final penetration depth. In a similar manner, anchors can be embedded using an impact or vibratory hammer in place of the suction force. There are also hybrid techniques that use combination of free-fall to an initial shallow direct-embedment depth followed by drag-embedment to the final design penetration depth.
Current gravity-embedment techniques deploy a free-fall anchor from a pre-determined height above the seafloor and use the momentum of the falling anchor to adequately embed the anchor into and below the seafloor. Often a deployment height above the seafloor is used that will allow the anchor to reach terminal velocity before penetrating the seafloor. In general, this height is 50 to 150 meters above the seafloor; in deep water it can take a significant period of time to rig the anchor and orient it above the target location.
Gravity-embedded anchors that have been employed in the past have included free fall anchors that glide down at an angle to the seafloor in lieu of dropping relatively straight down to the seafloor. In some current configurations, gravity-embedded anchors are used that look much like darts or torpedoes. An exception to the free-fall anchor type is an anchor that uses a so-called flexible gravity follower to slowly push the plate anchor mounted on the follower tip to final penetration depth by means of the follower's dead weight only. Conventional gravity-embedded free-fall anchors are passively-stabilized with fixed and non-movable stabilizing fins.